Fate/Zero
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Fate/Zero is a light novel by Gen Urobuchi, illustrated by Takashi Takeuchi, and is a prequel to all routes in Type-Moon's visual novel, Fate/stay night.

The story of Fate/Zero takes place ten years prior to the events of Fate/stay night, detailing the events of the Fourth Holy Grail War in Fuyuki City. The Holy Grail War is a contest, founded by the Einzbern, Matou, and Tōsaka families centuries ago, in which seven mages summon seven Heroic Spirits to compete to obtain the power of the "Holy Grail", which grants a wish to each member of the winning duo. After three inconclusive wars for the elusive Holy Grail, the Fourth War commences (Wikipedia).